The present invention relates broadly to the general field of electro-optical equipment and more particularly, to a highly responsive electronic image motion compensation system which is capable of electronically compensating for unwanted vibrations of the optical equipment over a wide frequency range to improve the quality of resolution of the target images projected on the receiving area of a TV camera included as part of the electro-optical equipment.
It is widely known that electro-optical equipment is being used to view objects as part of surveillance and guidance assist mechanisms for both stationary and mobile devices, such as aircraft, missiles, robots and the like. Electro-optical equipment used for these purposes generally comprise a conventional TV camera including an image intensifier portion; and a number of optical elements for optically guiding the line-of-sight of the TV camera to a predetermined target object, thereby projecting the target images(s) on the picture receiving area of the TV camera. In some electro-optical systems, a scan of the viewing field of the TV camera is accomplished with the implementation of at least one movable image reflector optical element, such as a mirror or prism, for example, which optically directs the line-of-sight path of the TV camera. Movable reflectors of this type are generally pivoted in one or more axes under the control of a gimballed mechanism as shown simply in FIG. 1.
Unwanted angular rotational movements of the reflector are normally caused by resonating vibrations and disturbances generated primarily from a stable body supporting structure. Unwanted movement of the reflector about the axis which is normal to both the incident and reflected line-of-sight paths (see FIG. 1) is the more difficult to mechanically stabilize mainly because unwanted reflector motions can exist in that axis while no corresponding motion occurs of the stable body, the body whose position is controlled by conventional stabilization systems. This phenomenon occurs when the structural members supporting the stable body and reflector experience angular perturbations not experienced by the TV camera system (see FIG. 1). These mechanically uncompensated vibrating angular rotations of the reflector optical element, result, in most cases, in blurred and fuzzy images at the receiving area of the TV camera. To overcome this mechanical stabilization problem, attempts have been made to compensate for this unwanted angular motion electronically, instead of mechanically, to prevent loss of resolution of the TV images within the TV camera resulting therefrom.
Electronic image motion compensation systems similar to the one disclosed in U.S. Pat. No. 3,641,261 entitled "Night Vision Systems", issued Feb. 8, 1972 to R. W. Chaplin et al. may be used for these purposes and may be comprised of a gyro mechanism disposed at a movable reflector to measure unwanted angular deflection of the reflector optical element and to generate signals representative thereof; and a plurality of electron beam deflection coils, which are positioned at the image intensifier portion of a conventional TV camera system, for canceling out the vibrating disturbances influencing the projected image within the TV camera intensifier as governed by the measurement signals of the gyro mechanisms.
One disadvantageous feature of this type of image motion compensator is that the gyro mechanisms used for measuring unwanted vibrating movement of the reflector element are somewhat limited in their measurement frequency bandwidth. Even the more precision and costly gyro mechanisms have only an effective bandwidth of 100 to 200 Hz while the less costly gyros may be limited to a bandwidth of merely 50 Hz or less. Since it is known that these optical reflector-type elements may incur, at times, vibrating disturbances in the frequency ranges above 200 Hz due to resonances developed in the structural support elements, for example, it appears that the electronic motion compensators of the type described supra may be inadequate, in all cases, to compensate for vibratory disturbances, especially those above 200 Hz. Therefore, one may still expect a loss of resolution in the TV picture manifested as blurred and fuzzy images which are passed uncompensated to the TV camera system as a result of the undetected higher frequency disturbances of the reflector element. Furthermore, these resulting blurred and fuzzy TV images on a per-frame basis may hamper any correlation operations, such as normally used in guidance assist type systems, for example, which require sharp, crisp and highly resolvable images. For this reason, it is felt that an improvement in the resolution quality of the image rendered by the electro-optical systems is of considerable importance to maintain the integrity of the highly sophisticated, automatic guidance and control systems normally connected therewith.
In some airborne applications of these electro-optical guidance assist mechanisms, packaging density of the equipment is constantly being reviewed for improvement. For example, in the aforementioned image motion compensation system, it has been noted that the gyro mechanisms used for measuring unwanted disturbances of the movable optical elements generally have approximate cylindrical packaging dimensions of one inch (2.54 cm) in diameter and two inches (5.00 cm) in length and usually weigh between 4 and 5 ounces (109 to 136 grams). It is felt by some that the functional purpose for which these gyros are used does not warrant such volume and weight especially in airborne applications and that in these cases, it would be desirable to facilitate the same function with a reduction in packaging density.
In view of the above, it is evident that known electronic image motion compensation systems could be improved to measure vibrating disturbances of the reflector optical element over a wider frequency range thus enhancing the capability of compensating for these vibrating disturbances to effectively increase the quality of resolution of the TV images. In addition, any size, weight and cost improvements of the image motion compensation systems will further increase their commercial attractiveness, especially their utilization in airborne guidance assist type systems.